A semiconductor device such as an LED or a power module has a structure in which a semiconductor element is bonded onto a circuit layer formed of a conductive material.
A power semiconductor element used for controlling the high power of wind power generation or electrical vehicles such as electric cars has a significant heating value. Accordingly, a ceramic substrate having excellent heat resistance and insulating properties, such as Si3N4 (silicon nitride), AlN (aluminum nitride), or Al2O3 (alumina) has been used as a substrate for mounting such a power semiconductor element. A power module substrate obtained by bonding a Cu plate having excellent electric conductivity to one surface of this ceramic substrate as a circuit layer has been widely used in the related art. A metal plate may be bonded to the other surface of a ceramic substrate.
In the related art, a so-called direct bonding copper (DBC) method of performing heating at a temperature equal to or higher than 1000° C. in the N2 atmosphere while applying loads to a ceramic substrate and a Cu plate in a state where the Cu plate is laminated on the ceramic substrate is known as a method of bonding a Cu plate to a ceramic substrate (for example, see PTL 1).